Hello,

Go to sys_sg_icon.list and find your icon. There you can change it, it is an icon field key named "BackgroundColor". Place inside the Hexadecimal color you want.

Please check the below post for the same:-

https://www.servicenow.com/community/mobile-apps-platform-forum/how-can-i-change-the-background-colo...

Please mark my answer as correct based on Impact.